investigation of properties of sol gel dip coated nickel doped metal sulphide (cds, cus, mgs) thin films for solar energy applications

Description

ABSTRACT

The paper presents an investigation of the properties of CdS, CuS, MgS thin films and their suitability for use as solar cell material. In this work, we have successfully fabricated undoped and Ni-doped CdS, CuS, MgS thin film on an ultrasonically cleaned glass substrate employing the Sol-Gel spin coating technique. The structural and spectroscopic properties of the films were investigated using XRD spectra, UV-Vis spectroscopy and photoluminescence spectra respectively. The X-Ray diffraction spectra revealed the polycrystalline nature of films with cubic structure and (111) as preferred orientation. The average particle size evaluated by the Debye-Scherrer formula lying in the range 6.65nm to 12.05 nm for the deposited films. According to UV-VIS Spectroscopy, the average transmittance of films in the visible region varies between 70% to 90%. The optical band gap of CdS, CuS, MgS thin film was evaluated from absorption spectra. The bandgap of the deposited films is in the range of 2.48 eV to 2.70 eV which is higher than that of bulk CdS (2.42eV). This verifies the blue shifting in band edge of CdS, CuS, MgS thin films due to the quantum confinement effect. Photoluminescence spectra of the thin film showed that the fundamental band edge emission peak centred at 485nm also called blue band emission.

Keywords: Thin films, Sol-Gel spin coating technique, solar energy application, doped metal sulphide.

 

TABLE OF CONTENTS

COVER PAGE

TITLE PAGE

APPROVAL PAGE

DEDICATION

ACKNOWLEDGEMENT

ABSTRACT

CHAPTER ONE

1.0      INTRODUCTION

• BACKGROUND OF THE STUDY
• AIM/OBJECTIVE OF THE STUDY
• SCOPE OF THE STUDY
• SIGNIFICANCE OF THE STUDY

CHAPTER TWO

LITERATURE REVIEW

• OVERVIEW OF METAL SULPHIDE USED
• THIN FILMS AND PROPERTIES
• BENEFITS OF THIN FILMS
• OPTICAL AND SOLID STATE PROPERTIES OF THIN FILM
• METHODS FOR THIN FILM GROWTH

 

CHAPTER THREE

MATERIAL AND METHOD

CHAPTER FOUR

RESULT AND DISCUSSION

CHAPTER FIVE

• CONCLUSION
• RECOMMENDATION

REFERENCES

CHPATER ONE

1.0                                                           INTRODUCTION

1.1                                            BACKGROUND OF THE STUDY

Energy keeps the world alive. It is an important index for evaluating a nation’s status as per capita of electrical energy. Energy can be classified into renewable and non-renewable. Non- renewable energy comprises of fossil fuels which come in three principal forms from which many other products are derived such as coal, crude oil and natural gas. With the fossil energy crisis in view and some international policies about oil, scientist all over the world turn their attention to developing an alternative energy resources that will augment the conventional energy sources to meet the world energy demands. Apart from the depletion of fossil fuel, it has also been recognized that heavy reliance on fossil fuel has had an adverse impact on the environment. For example, gasoline engines and steam-turbine power plants that burn coal or natural gas send substantial amount of sulphur dioxide (SO₂) and nitrogen oxides (NO₂) into the atmosphere.

When these gases combine with atmospheric water vapour, they form sulphuric and nitric acids, giving rise to acidic precipitation which endangers plants and animals. Furthermore, the combustion of fossil fuels also releases carbon dioxide into the atmosphere; the amount of this gas in the atmosphere has been observed to have steadily risen since the mid-1800, largely as a result of the growing consumption of coal, oil and natural gas. More and more scientists believe that the atmospheric buildup of carbon dioxide (with that of other industrial gases such as methane and chlorofluorocarbon) may induce greenhouse effect, causing rise in the surface temperature of the earth by increasing the amount of heat trapped in the lower atmosphere. This condition could bring about climate change with serious repercussions for natural and agricultural ecosystems. Renewable energy is inexhaustible as the material producing it is replenishable. Such renewable energy sources include Biomass, wind, marine, geothermal, oceanic/tidal, hydro-power and solar energy.

Solar energy is energy from the sun produced in the sun’s thermonuclear reactor where two reactions- proton-proton and Bethe cycle reactions take place with helium molecule as the end product. This radiated in different direction in the form of electromagnetic waves (sun rays) within spectrum of Ultraviolet (UV) of wavelength 0.3 -0.4µm, Visible of wavelength 0.4 – 0.74µm and Infrared (IR) of wavelength 0.74 – 4.0µm. The average amount of solar energy radiated to earth is about 1360 kW/m² depending on latitude and regional weather pattern (Green, 2001) and such parameters as: cloudiness index, clearness index, turbidity, albedo, transmittance, absorbance and reflectivity. Solar energy is very viable in Nigeria because her average sun hour is about 4.5 hours. However, the energy from the sun can be trapped directly as thermal energy using thermal collectors or directly to electricity (direct current) using photovoltaic cell (solar cells) arranged in arrays to form solar panels. The solar cells are made from semiconductors which act as non-conductor at room temperature and conductor above room temperature. Semiconductor could be single such as Silicon wafer or compound semiconductors (binary, Tennary, etc). Because of cost of solar panel due to high cost of silicon wafers, search for possible cheap alternative cells for the fabrication of solar panels using thin films is on the increase and that is why we have joined the numerous scientists undertaking research in thin film technology.

Thin films are crystalline or non-crystalline materials developed two dimensionally on a substrate’s surface by physical or chemical methods. They play vital role in nearly all electronic and optical devices. They have been used as electroplated films for decoration and protection (Heaven, 2010). They have long been used as anti-reflection coatings on window glass, video screens, camera lenses and other optical devices. These films are less than 100 nm thick, made from dielectric transparent materials and have refractive indices less than that of the substrate (Pentia, et al, 2014). However, the use of techniques which have been developed over the last few years show that much of the thin films are of recent origin. Thin films of thickness less than 100 nm now serve as anti-reflection coatings on solar energy collectors. Thin semiconductor films on metal or glass substrate form a promising type of low cost solar cells.

In industrial, scientific and technical applications of thin films, their physical properties such as optical, chemical, electrical etc are investigated and the results are applied in several devices such as solar energy devices, xerography, switching devices, high resolution lithography, optic memories, photo-detectors etc.

Thin films deposition for optical, electronic and optoelectronic device application has become an industry in most advanced countries using highly technological, sophisticated and very expensive techniques. However, in the third world countries, the high technological and sophisticated techniques are not easily achieved because of their complexity and the poverty of the third world countries. Hence, considerable efforts are put into developing simple and cheap techniques of depositing thin films. The solution growth technique offers the simplest, cheapest, most economical and affordable method of depositing thin films like Halide and Chalcogenide.

The Cadmium Sulphide (CdS), Copper sulphide (CuS) and Magnesium sulphide (MgS) among the binary group semiconductors II-IV are considered among the favorable candidates in thin films based solar cells (Mahmood et al., 2018). They are used as a window layer with many absorber layers in thin films based solar cells. These metal sulphide layers have good transparency and characterized by a direct band gap, with a wide gap band (Moualkia et al., 2009) and n-type conductivity. All these characteristics make them the most potential candidate as an optical window in

solar cells. The electrical conductivity is a very important parameter in thin films based solar cells. For this reason, the enhancement of electrical conductivity for these metal sulphide thin films allows having an improvement of the cell performance. Therefore, the control of native faults makes it possible to command the electrical properties of metal sulphide. The electrical conductivity of metal sulphide layers should be improved to aggrandize the conversion efficiency of solar cells.

The several statues in literature have investigated the doping with two element of metal sulphide thin films.

In literature, many physical and chemical methods are used to synthesize CdS thin films. For example, sol gel dip coating (Soussi L et al., 2018), spray pyrolysis (Sivaraman et al., 2014), chemical bath deposition (CBD) (Maghouli et al., 2019) chemical vapor deposition (CVD) (Chenthamarai et al., 2000), spin coating (Al-Douri et al., 2015). Sol gel spin coating is a simple chemical technique to perform which does not require vacuum conditions. On the other hand, sol-gel coating has drawn much attention to prepare thin films with high quality, minimum defects, and great adhesion to substrates.

In this study, we are interested in investigating the properties of Cadmium Sulphide (CdS), Copper sulphide (CuS) and Magnesium sulphide (MgS) thin films that make them suitable for solar applications.

1.2       AIM AND OBJECTIVES OF THE STUDY

The main aim of this work is to present an investigation of the properties of Cadmium Sulphide (CdS), Copper sulphide (CuS) and Magnesium sulphide (MgS) thin films and their suitability for use as solar cell material. The objectives of the study are:

1. To carry out an experiment that will determine their suitability for use as solar cell material using sol gel based dip coating process in order to investigate their optical, structural and electrical properties.
2. To present some findings on how to optimize the sol gel based dip coating process to achieve improved quality of these metal sulphide thin films deposited on glass substrates.

1.3       SCOPE OF THE STUDY

In this work, Nickel doped CdS, CuS, MgS thin films and powders have been prepared on glass substrates using sol gel based dip coating process in order to investigate their optical, structural and electrical properties. All the samples were tested to investigate the physical, electrical and optical characteristics of the deposited thin films. The physical properties measured were the thickness and surface morphology of the samples. The electrical properties were the resistivity, conductivity type and charge carrier mobility while the optical property was the band gap energy.

1.4       SIGNIFICANCE OF THE STUDY

This study shall serve as a means of making the reader of this thesis to become familiar with Nickel doped CdS, CuS, MgS thin films.

This study will also help the student involved to observe properties exhibited by the deposited thin films of metal sulphide (CdS, CuS, MgS thin films) that make the films good materials for many optoelectronic and electronic applications such as solar cell.

REFERENCES

Heavens, O. S. (2010), Thin film Physics, Methuen and Co Ltd. London

Pentia, E., V. Draghici, G. Sarua, B. Mereu, L. Pintilie, F. Sava and M. Popescu (2014) Structural electrical and photoelectrical properties of Cd_xPb_1-xS thin film prepared by chemical bath deposition, J. Electrochem. Soc. Vol. 151 (11) 729-733

Mahmood W, Ali J, Zahid I, Thomas A and ul Haq A 2018 Optical and electrical studies of CdS thin films with thickness variation Optik (Stuttg). 158 1558–66

Moualkia H, Hariech S and Aida M S 2009 Structural and optical properties of CdS thin films grown by chemical bath deposition Thin Solid Films 518 1259–62

Soussi L et al 2018 Structural, optical and electrical properties of pray pyrolysis deposited CdS:Fe thin films Proc. 2018 6th Int. Renew. Sustain. Energy Conf. IRSEC 2018 p 17

Sivaraman T, Balu A R and Nagarethinam V S 2014 Effect of magnesium incorporation on the structural, morphological, optical and electrical properties of CdS thin films Mater. Sci. Semicond. Process. 27 915–23

Maghouli M and Eshghi H 2019 Effect of deposition time on physical properties of nanostructured CdS thin films grown by chemical bath deposition technique Superlattices Microstruct. 128 327–33

Chenthamarai S, Jayaraman D and Subramanian C 2000 Nucleation kinetics of cadmium sulphide thin film – CVD technique Mater. Chem. Phys. 63 163–6

Al-Douri Y and Reshak A H 2015 Analytical investigations of CdS nanostructures for optoelectronic applications Optik (Stuttg). 126 5109–